Enhanced Privacy Identification (EPID) is a digital signature scheme. A group public key in EPID corresponds to multiple private keys. A private key can be used to generate a signature. The signature can be verified using the group public key.
EPID is an extension of Direct Anonymous Attestation (DAA). DAA is a cryptographic scheme for providing anonymous signatures. DAA is used for the Trusted Platform Module created by the Trusted Computing Group.
A feature of EPID is that keys issued can be blind. The issuer need not know a member's private key. The EPID signatures are anonymous. The EPID signature cannot be opened to identify the member. The linkability of an EPID signature and members of a group depend upon the base values that are chosen and revealed during the signature. Signatures using a common name verifier can be linked. A signature using a random signature cannot be linked. Signatures using different name verifies cannot be linked. EPID signatures or keys can be revoked.